The demo does not have any efficient engines. Just the LV-T30 and some boosters IIRC. It's still possible to build a rocket that orbits, gets to the Mun, lands and returns in the demo though. I would suggest utilizing the build tools in the top left to offset your engine into the fuel tank so that the lander legs will work properly. Of course if you're just wanting to orbit, try this: command pod with parachute, small inline reaction wheel, 2 tanks, engine, decoupler, 10 tanks, engine. No fins or boosters. Press T and space, it should go straight up. At 7000M pitch slowly on the 90 degree vector. Not too fast. The first stage should get you to space, second stage to circularize, and there should be more than enough fuel to return. I just tested this exact rocket in the demo, and it worked just fine even though my orbit was terrible and I wasted a crap ton of fuel. Hope that helps.